Abstract
Purpose:To evaluate dosimetric uncertainty in 4D dose calculation for lung cancer patients using three different temporal probabilities.Methods:The impact of temporal probability, defined as the fraction of time a patient spends in each respiratory amplitude, was evaluated in nine lung cancer patients. For each patient, 4D dose was computed using 4DCT and three temporal probability distributions: 1) uniform distribution, 2) sinusoidal distribution, and 3) patient‐specific distribution. To calculate 4D dose, the dose for each of 10 binned CTs was first computed using the same planning parameters as those used in the breath‐hold CT. Next, deformable image registration was used to deform the dose of each binned CT to the breathhold CT using the deformation map between each binned CT and the breathhold CT. Finally, 4D dose volume was computed by summing the 10 deformed doses using corresponding temporal probabilities. In this study, 4D dose calculated from patient‐specific temporal probabilities was used as the ground truth. Dosimetric comparison included: 1) 3D gamma (3% dose difference, 3mm distance to agreement tolerance), 2) mean tumor dose (MTD), 3) mean lung dose (MLD), and 4) lung V20.Results:For all patients, both uniform and sinusoidal dose distributions were found to have an average gamma passing rate >99% for both lung and PTV volume. Compared with 4D dose calculated using the patient respiratory trace, uniform distribution and sinusoidal distribution showed a percentage difference on average of ‐0.1±0.6% and ‐0.2±0.4% in MTD, ‐0.2±2.0% and ‐0.2±1.3% in MLD, 0.9±2.8% and ‐0.7±1.8% in lung V20, respectively.Conclusion:Both uniformly and sinusoidally‐distributed temporal probabilities can be used to approximate 4D dose calculation. The dosimetric difference among the three temporal probability distributions is not clinically significant.This research is supported by Siemens Medical Solutions USA, Inc
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